Search Results (69)

Based on the engineering background of a new type of segmental-assembled steel temporary beam buttress, the fatigue strength evaluation method of the steel box girders with open longitudinal ribs was taken as the research objective. The fatigue stress calculation analysis and the full-scale fatigue loading test for the steel box girder local component were carried out. The accuracy of the finite-element model was verified by comparing it with the test results, and the rationality of the fatigue strength evaluation methods for welded joints was deeply explored. The results indicate that the maximum nominal stress occurs at the weld toe between the transverse diaphragm and the top plate at the edge of the loading area, which is the fatigue-vulnerable location for the steel box girder local components. The initial static-load stresses at each measuring point were in good agreement with the finite-element calculation results. However, the static-load stress at the measuring point in the fatigue-vulnerable position shows a certain decrease with the increase in the number of cyclic loads, while the stress at other measuring points remains basically unchanged. According to the finite-element model, the fatigue strengths obtained by the nominal stress method and the hot-spot stress method are 72.1 MPa and 93.8 MPa, respectively. It is reasonable to use the nominal stress S-N curve with a fatigue life of 2 million cycles at 70 MPa and the hot-spot stress S-N curve with a fatigue life of 2 million cycles at 90 MPa (FAT90) to evaluate the fatigue of the welded joints in steel box girders with open longitudinal ribs. According to the equivalent structural stress method, the fatigue strength corresponding to 2 million cycles is 94.1 MPa, which is slightly lower than the result corresponding to the main S-N curve but within the range of the standard deviation curve. The research results of this article can provide important guidance for the anti-fatigue design of welded joints in steel box girders with open longitudinal ribs. Full article

In deep foundation pit engineering, the rational arrangement of internal struts plays a crucial role in controlling diaphragm wall displacement and minimizing environmental impacts. This study investigates the effects of servo steel struts through model tests, analyzing diaphragm wall displacement, bending moment, surface settlement, and surrounding soil pressure during both excavation and active servo control phases. The results show that installing servo struts near the pit bottom significantly improves deformation control, whereas strut placement in shallow zones more effectively mitigates surface settlement. The servo system dynamically adjusts strut displacements, thereby inducing internal force redistribution in the diaphragm wall and modifying the stress field in surrounding soils. This mechanism leads to an increase in positive bending moments on the wall’s backside, which may necessitate the localized reinforcement of the diaphragm wall at servo strut connections to ensure structural integrity. The lateral wall and surrounding soil pressure exhibit further increase, effectively compensating for the pressure loss induced by excavation unloading. Notably, the influence on soil pressure demonstrates a dissipating trend with an increasing distance from the excavation. Full article

Uniformity in material coating is not only essential for ensuring durability and long-term reliability but also for reducing costs, optimizing resources, and maintaining high-quality standards in industrial applications. Zinc phosphate is notable for coating steel surfaces due to its excellent corrosion resistance and adhesion properties in various industries. This study investigates the optimal flow rate of a diaphragm pump for achieving the effective and uniform coating of a steel cylinder. The coating uniformity was assessed using Scanning Electron Microscopy (SEM), focusing on layer thickness and elemental composition. A range of flow rates was analyzed to determine their influence on coating quality and regularity, with Energy-Dispersive Spectroscopy (EDS) revealing the distribution and homogeneity of the applied layer. The results identified a flow rate of 30 L/min as optimal with a thickness of 3.6 µm of coating on both sample sides, as it minimized surface defects and ensured consistent thickness across the cylinder. This study provides valuable insights for optimizing industrial coating processes, contributing to improved efficiency and reduced resource waste. Full article

Multi-cavity double steel plate–concrete composite structures are composed of two layers of steel plates, accompanied by steel flanges, diaphragms, and a core of concrete. Thanks to their exceptional mechanical attributes, these structures have gained widespread adoption in the field of wind power engineering. The outer steel plates exert a notable confinement on the concrete filling. Nonetheless, there remains a lack of a constitutive model specifically tailored for concrete under confinement within the field of multi-cavity double steel plate–concrete composite structures. To bridge this gap, our research endeavor involved the creation of approximately 2000 shell–solid finite element models, leading to the derivation of a constitutive model for compressed confined concrete within such structures through regression analysis. Initially, theoretical evaluations were conducted to pinpoint the structural parameters potentially influencing confinement behavior. Thereafter, Abaqus shell–solid finite element models were formulated, and their accuracy was corroborated through experimental validations. By systematically adjusting parameters in batch modelling, regression analysis was conducted. Consequently, a constitutive model tailored for uniaxial compression of concrete in multi-cavity double steel plate–concrete composite structures (MDSCCS) was formulated. According to the results, the strength of confined concrete in MDSCCS can be enhanced by up to 23% under typical configurations, as observed in the benchmark model MDSCCS-1. The proposed regression-based confinement model demonstrates a prediction error of less than 15% in 97.8% of the 1342 finite element models that successfully converged in batch simulations. Full article

Localized diaphragm (transversal plate) deformation and buckling were identified at the arc notch region during structural inspections of an operational steel bridge. To evaluate the potential structural consequences, alterations in the fatigue performance and stress characteristics induced by this deformation were systematically investigated through in situ monitoring combined with numerical simulation. It was demonstrated that the global load-transfer mechanism of the orthotropic steel deck (OSD) system remained minimally compromised. While within the localized deformation zone, the stress magnitudes at the diaphragm-to-U-rib (DU) welds were observed to be significantly amplified, and the stress concentration zones were found to be relocated to geometrically depressed regions. Based on the deformation-stage mechanical responses, the strategic employment of residual compressive stress generated through controlled hammer peening was proposed for counteracting stress escalation at DU welds recently caused by diaphragm buckling, whereas steel plate reinforcement strategies were recommended for mitigating progressive deformation development. Full article

Based on the engineering context of prefabricated underground station structures, this paper proposed a novel diaphragm wall–beam joint based on post-poured ultra-high-performance concrete (UHPC) and non-contact lap-spliced steel bars. This research study designed and conducted a full-scale experiment on the diaphragm wall–beam joints. The failure modes, bearing capacity, overall stiffness, crack resistance performance, and force transmission mechanism of the new diaphragm wall–beam joint were investigated. Additionally, a three-dimensional finite element model (FEM) of the wall–beam joint was developed using the software ABAQUS 2020. The model was validated against experimental results and used for further analysis. The results showed that the tensile through-cracks at the UHPC-diaphragm wall interface characterize the final failure process. The proposed UHPC joint could satisfy the structural design requirements in terms of crack resistance and bearing capacity. No rebar pulled-out damage was observed, and the non-contact lap-spliced length of 10d in the UHPC joint was sufficient. Compared with the traditional cast-in-place concrete joint, the cracking moment and yield moment of the proposed UHPC joint increased by 8.7% and 5.4%, respectively. Full article

This paper is focused on the numerical evaluation of the equivalent damping ratio (EDR) given by a dissipative wood-based roof diaphragm in the seismic retrofitting of single-nave historical churches. In the design phase, the EDR could be a key parameter to select the optimal roof structure configuration, thereby obtaining the maximum energy dissipation. In this way, the roof structure works as a damper to facilitate a box behavior of the structure during the seismic response. The EDR measures the energy dissipated by the nonlinear behavior of the roof’s steel connections and masonry walls during seismic events. In a preliminary retrofitting design phase, an initial implementation of the geometries of the walls and the chosen geometry for the roof is carried out by adopting an equivalent frame model (FEM) with inelastic rotational hinges for the nonlinear properties of the masonry walls and inelastic shear hinges for the nonlinear behavior of the roof’s steel connections. Since, for historical churches, the transversal response under seismic events is the worst situation for the single-nave configuration, the earthquake is applied as transversal accelerograms. In this way, the damped rocking of the perimeter walls due to the dissipative roof diaphragm can be described in terms of a hysteretic variable. By varying the value of the hysteretic variable, possible configurations of the roof diaphragm are tested in the design phase, considering the different shear deformation values of the inelastic hinges of the roof. Under these hypotheses, the EDR is evaluated by performing nonlinear Time History analyses based on the cyclic behavior of the inelastic hinges of the roof, the strain energy contribution due to the walls, and the lateral displacements of the structure. The EDR values obtained with the Time History method are compared with those obtained by applying the Capacity Spectrum Method by performing nonlinear static analyses, either for the coefficient method of FEMA 356 or the equivalent linearization technique of ATC-40. The EDR evaluations are performed by considering the following different hysteretic behaviors of the roof’s steel connections: the skeleton curves with stiffness degradation and the trilinear model with strength and stiffness degradation. Finally, the variation in the EDR values as a function of the hysteretic variable is presented as well so to evaluate if the maximum EDR value corresponds to the optimal value of the hysteretic variable able to reduce the lateral displacements and to contain the shear forces acting on the roof and the façade under a safety limit. Full article

Partially concrete-filled steel tubes (PCFSTs) are often used to reduce the dead weight of concrete-filled steel tubes (CFSTs). Most previous studies have focused on the presence or absence of diaphragms directly above the concrete filling of PCFSTs, and few have focused on diaphragm characteristics. Therefore, this study presents the parametric analysis of partially concrete-filled steel tubes with circular cross-sections to clarify the effect of the diaphragm’s parameters on the horizontal load capacity. The authors performed pushover analyses for a total of 84 cases, focusing on four axial force ratios, three diaphragm thicknesses, and seven diaphragm opening ratios. Although the thickness of the diaphragm had little effect on the horizontal load capacity, the opening ratio affected the horizontal load capacity. It was found that an opening ratio of 40–80% provided a higher horizontal load capacity than the 20%, 90%, and 95% openings. Full article

To enhance the standardization and construction efficiency of prefabricated steel structures and to promote the application of cold-formed steel tubes with the advantages of high standardization, superior mechanical properties, and fast processing speeds, two types of composite beam to concrete-filled cold-formed high-strength square steel tubular column joints with different connection forms were designed in this study: the external diaphragm joint (ED joint) and the through diaphragm joint (TD joint). These joints were subjected to cyclic loading tests to evaluate the influence of the connection designs on key seismic performance parameters, such as failure modes, load-bearing capacities, the degradation of strength and stiffness, ductility, and energy dissipation capabilities. The results show that both the ED and TD joints experienced butt weld fractures at the bolted-welded connections on the beam, effectively transferring the plastic hinges from the joint zone to the beam and demonstrating good seismic performance. The ED joint specimen JD1 and the TD joint specimen JD2 exhibited similar load-bearing capacity, stiffness, strength degradation, and energy dissipation capacity. However, the TD joint showed lower ductility compared to the ED joint due to premature weld fractures. A nonlinear finite element model (FEM) was developed using MSC.MARC 2012, and the numerical simulation showed that the FEM could effectively simulate the hysteresis performance of the composite beam to concrete-filled, cold-formed, high-strength, square, steel tubular column joints with external and through diaphragms. Full article

The steel box girder bridge is a structure composed of mutually vertical stiffening ribs (longitudinal ribs and transverse ribs) that carry the loads of vehicles. Since the external loads are usually complex and variable, the rational design of the bridge components is a topic that deserves more attention. The purpose of this study is to explore the optimal range of some of the component design parameters, expecting to reduce costs while ensuring the stress-carrying capacity. A finite element model (FEM) based on ABAQUS was built and the results were verified by laboratory experiments. The varied thicknesses of the bridge deck, diaphragm, and U-rib were explored based on the validated FEM. The simulation results fit well with the experimental results, which proved that the FEM was quite reliable. The stress analysis results demonstrated an optimal range of 18–20 mm for bridge deck thickness, 14–16 mm for diaphragm thickness, and 8–10 mm for U-rib thickness. The present study holds significant reference value for the design and optimization of multiple steel box girder bridge components, which could further provide a theoretical foundation for related research in this field. Full article

Curved continuous steel box girders are extensively utilized in bridge construction due to their efficiency and environmental benefits. However, in regions with significant temperature fluctuations, temperature effects can result in cumulative deformation and stress concentration, which may severely impact structural safety and durability. This study examines the structural response of curved continuous steel box girders with five spans under diverse temperature conditions and also develops a comprehensive parameterized thermodynamic numerical model. The model assesses the influence of cross-sectional shape parameters, including the number of cross-sectional box chambers, diaphragm thickness, and height-to-width ratio, as well as longitudinal structural parameters such as planar configurations, width-to-span ratio, and support arrangements, along with the arrangement of stiffening ribs on the temperature-induced effects in the girders. The results indicate that optimizing the width and eccentricity of support stiffeners to 30% and 25%, respectively, in support plate size can significantly alleviate local temperature-induced stresses. Additionally, variations in longitudinal and transverse stiffeners manifest minimal impact on thermal performance. These findings provide a theoretical foundation for improved design and construction practices, offering practical design recommendations to mitigate temperature effects and enhance the longevity and safety of such structures. Full article

Traditional numerical analyses often overlook the potential impact of adjacent building basements on ground surface deformation. This study investigated the influence of neighboring structures on diaphragm walls and ground surface deformation during deep excavation for building foundations using PLAXIS 3D finite element software. This study simulated the top–down construction method with plate elements for diaphragm walls retaining H-shaped steel for support and pre-stressed anchors. The adjacent structures were modeled using plate elements. Numerical analysis results were compared with field observations for model validation. The results show that the lateral displacement of the retaining wall varies with the depth of neighboring basements. At 0.5 times the excavation depth, displacement was significant, and it stabilized at 1.0 times the depth. When the distance between adjacent buildings and the retaining wall was about twice the excavation depth, the deformation curve converged, indicating negligible influence beyond this distance. Ground surface settlement increased as the neighboring basement depth reached half the excavation depth, and stabilized at 1.6 times the depth. A closer proximity resulted in greater ground surface settlement. These findings offer practical references for deep excavation design and assessment, aiding engineers in ensuring project stability and safety. Full article

In order to investigate the coordinated relationship between lateral deformation of the diaphragm wall and axial force of the internal strut, this paper first carried out a scaled model test on the mechanical features of a foundation pit support system based on a novel axial force servo device. Then, a finite element model was established to simulate the scaled model test, and the correctness of the finite element modeling approach was validated by comparing test results. After that, the same finite element modeling method was used to analyze the coordinated relationship between axial force and lateral deformation in the prototype foundation pit support structure. The results show that the axial force of the inner strut is negatively correlated with the lateral deformation in the diaphragm wall. The initial maximum lateral deformation in the diaphragm wall of the shaft foundation pit occurs at the bottom of the foundation pit, so changing the length of bottom strut simultaneously is the most effective way to adjust the mechanical behavior of the support structure. Under various support conditions, the maximum lateral deformation of the diaphragm wall in the prototype project is 0.59~0.66‰ of the total excavation depth of the foundation pit, and the maximum axial force of internal support is 11~30% of the yield load of a single steel strut. Full article

To study mechanisms of jet atomization, a novel method of experimentation utilizing the resonation of diaphragms made from thin steel plates has been previously developed. In the experiments, a diaphragm covered by a film of water emitted acoustic sounds, and jet atomization from the water film was observed. Experiments using diaphragms composed of different materials and fast Fourier transformation analysis of the acoustic sound revealed that jet atomization occurred under limited surface conditions of the diaphragm and a specific range of frequency. In this article, the dynamics of a resonating body composed of the diaphragm and water film were analyzed using the finite element method with a combination of theoretical analyses of surface waves of water, such as the well-known Lang’s equation. The present FEA results, from harmonic response analyses with consideration of viscous damping effect due to interaction between the diaphragm and water film, precisely confirmed the results of FFT analysis previously obtained by the experiment. Specifically, the peak frequency of the frequency response agreed well with the FFT results, and the shift of the peak frequency and attenuation due to the interaction in the analyses corresponded with the difference in surface conditions between the hydrophilic and hydrophobic materials of the diaphragm in the experiments. Our interpretation of the mechanism of jet atomization is expanded by the present numerical results. Full article

To address the issue of insufficient transverse connectivity in prestressed concrete box girder (PCB) bridges, this study investigates two transverse strengthening methods—installing diaphragms and utilizing concrete-filled steel tube trusses (CFSTTs). A finite element model was developed for a typical 30 m PCB bridge and was validated by on-site load test results for reliability. Based on the deflection and load distribution of PCB bridges before and after reinforcement, as well as the maximum stress and strain of the diaphragms and the CFSTTs, comparative analyses were conducted on diaphragms of different thicknesses and materials, as well as on CFSTTs of various strength grades. The results show that the addition of a transverse partition and CFSTTs can effectively improve the load distribution of the PCB bridge and reduce the maximum deflection of the girder, especially when using the CFSTT reinforcement method. The unique structural design improves the reinforcement effect of the material in the post-elastic stage. When using CFSTTs, increasing the steel tube wall strength significantly reduces the maximum deflection of the main girder. For example, using steel tubes with yield strengths of 235 MPa and 420 MPa filled with concrete of 50 MPa compressive strength reduced the maximum deflections by 15.32% and 24.55%, respectively, and improved the load distribution coefficients by up to 7.31% and 11.57%. Additionally, steel diaphragms demonstrated better reinforcement effects compared with concrete diaphragms. The load transverse distribution coefficients for the CFSTT-reinforced PCB bridge were calculated using the hinge plate (beam) and the rigid plate (beam) methods, showing minimal differences between the two approaches. The findings of this study provide valuable insights into the design of diaphragm and CFSTT reinforcement in PCB bridges, aiding in the selection of optimal reinforcement strategies. Full article